A dental technician from 4th Dental Battalion treats a Marine patient in a field dental suite in Senegal during a 2012 training exercise. (Sgt. Tatum Vayavananda/Marine Corps)

Members of a Marine reserve unit were called in for an emergency blood draw in late January after officials discovered that some had undergone dental examinations with unsterilized instruments during a drill weekend.

A group of 101 Marines from the Headquarters and Service Company of 1st Battalion, 23rd Marines — a 4th Marine Division unit headquartered in Houston — underwent dental exams administered by technicians from the 4th Marine Logistics Group’s 4th Dental Battalion Jan. 10-11. A spokesman for Marine Forces Reserve, Col. Francis Piccoli, said officials believe dental technicians inadvertently used unsterilized equipment on 45 of the Marines.

Local news station KRGV reported that the exams happened at the unit’s Harlingen, Texas, depot on Jan. 11. Officials learned about the incident four days later, the station reported.

It’s unclear how the mistake involving the unsterilized equipment took place.

Since officials said they have no way of knowing which of the 101 Marines were examined with the unsterilized tools, the unit notified all of them, through their platoon commanders, about the incident and asked them to report for a blood draw Jan. 18.

Capt. Cheryl Dengler, a Marine spokeswoman, said all 101 Marines were successfully contacted and reported for the blood draw. The results of that initial test, she said, are not yet in.

Following the blood draw, officials said, the Marines will be placed on a medical surveillance program for a year to monitor potential exposure to blood-borne pathogens. The initial blood draw will be followed up with subsequent draws at the one, three, six, nine and 12-month marks to identify, as quickly as possible, any blood-borne diseases the Marines might have contracted.

“The commanding general of the 4th Marine Logistics Group [Brig. Gen. Roger R. Machut] directed an investigation into the circumstances surrounding this event,” Piccoli said in an email. “Immediately, 4th Dental Battalion will be examining support-request procedures, transitioning to disposable equipment, and conducting extensive training with their personnel to ensure this does not happen again.”